1. Field of the Invention
The present invention relates to an amplitude modulated high frequency signal detection device, and more specifically to a device for detecting a playback high frequency (referred to as HF hereinafter throughout the specification) signal, to be used in a system for playing back recorded information, such as an optical video disc player system in which an amplitude modulated HF signal is detected when a pickup is moved across a plurality of record tracks.
2. Description of Background Information
In playback systems or record/playback systems such as optical video disc player systems, an HF pickup output signal is amplitude modulated when the pickup is moved across the record tracks, i.e., along a direction perpendicular to the record tracks. This amplitude modulated HF signal is then treated by a signal detection device in which the envelope of the input HF signal is compared with a reference signal to produce a detection signal. The output signal of the detection device is, for example, used as an input signal of a pickup position control device. In the signal detection device, the reference signal is produced also from the HF input signal using a voltage divider circuit responsive to peak values of the HF signal.
A shortcoming of the conventional HF signal detection device is that the detection of the signal may sometimes be difficult in such an occasion that the polarity (or the side where its envelope has higher amplitude than the other side with respect to the central level of the HF signal) is reversed, or if a time constant of a pre-processing stage is too small.
Further, there was another problem that the duty ratio of the detection signal is affected by a change in the relative speed between the pickup and the record tracks on the recording disc. Thus, in conventional detection devices, there was necessarily an error between the actual position of the pickup and the edge positions of the detection signal due to the change in the relative speed between the pickup and record tracks.